1. Field of the Invention
The present invention relates to a waveform sampling apparatus for A/D converting a fixed repeat-cycle analog input voltage.
2. Description of the Prior Art
FIG. 1 shows an example of a conventional waveform measuring system comprising a integrator circuit and an A/D converter.
In FIG. 1, the waveform measuring system consists of an integrator circuit 101, a digitizing circuit 102 and a gate controller 103 which are connected to a CPU 104 via a CPU bus. A memory 105 and a display device 106 and such like are also connected via the CPU bus to the CPU 104.
The integrator circuit 101 is a well known integrator circuit in which an analog voltage is integrated by controlling the ON/OFF state of a integrator gate. In the integrator circuit 101, integrator gate ON/OFF control; integration is performed while the integrator gate is ON and the integral is outputted while the gate is OFF. The digitizing circuit 102 digitizes the integral outputted from the integrator circuit 101. The gate controller 103 controls the ON/OFF state of the integrator gate in the integrator circuit 101 by outputting a gate control signal to the integrator circuit 101.
The CPU 104 uses software processing to data-process the value digitized by the digitizing circuit 102, displays the processed result on the display screen 106 and stores it in the memory 105. Data processing performed here is for instance processing to determine the average value of multiple waveform measurements of an analog input voltage.
In the above-mentioned waveform, measuring system, for an analog input signal with a repeat-cycle T' as shown in FIG. 2, integration is carried out during integration time T1 during which the integrator gate is ON; the integral is output and the integrator is reset during reset time T2 in which the integrator gate is OFF.
The waveform measuring system described above has the following disadvantages.
It is desirable to be able to set the integration period T, which consists of integration time T1 and reset time T2, to a value (e.g. 500 ms, 1.0 s, 10 s or such like) in accordance with the cycle of the analog output voltage of the device being measured. In a conventional waveform measuring system the circuit configuration of the gate controller and integrator circuit required in order to vary the integrator period T to a discretionary value has been complex.
In addition, problems such as leaks in the integrator circuit and overflow in the digitizing circuit have occurred when the integrator time T1 has been set to a long time, and these elements are unfortunately included in the data outputted after A/D conversion.